Technology is advancing at an unprecedented pace. For example, access to vast quantities of information through a variety of different communication systems are changing the way people work, entertain themselves, and communicate with each other. As a result of increased telecommunications competition mapped out by Congress in the 1996 Telecommunications Reform Act, traditional cable television program providers have evolved into full-service providers of advanced video, voice and data services for homes and businesses. A number of competing cable companies now offer cable systems that deliver all of the just-described services via a single broadband network.
The wireless device industry has recently seen unprecedented growth. With the growth of this industry, communication between wireless devices has become increasingly important. There are a number of different technologies for inter-device communications. Radio Frequency (RF) technology has been the predominant technology for wireless device communications. Alternatively, electro-optical devices have been used in wireless communications. Electro-optical technology suffers from low ranges and a strict need for line of sight. RF devices therefore provide significant advantages over electro-optical devices.
Conventional RF technology employs continuous sine waves that are transmitted with data embedded in the modulation of the sine waves' amplitude or frequency. For example, a conventional cellular phone must operate at a particular frequency band of a particular width in the total frequency spectrum. Specifically, in the United States, the Federal Communications Commission has allocated cellular phone communications in the 800 to 900 MHz band. Generally, cellular phone operators divide the allocated band into 25 MHz portions, with selected portions transmitting cellular phone signals, and other portions receiving cellular phone signals.
Another type of inter-device communication technology is ultra-wideband (UWB). UWB wireless technology is fundamentally different from conventional forms of RF technology. UWB employs a “carrier free” architecture, which does not require the use of high frequency carrier generation hardware, carrier modulation hardware, frequency and phase discrimination hardware or other devices employed in conventional frequency domain communication systems.
Regardless of the communication technology that is employed, today's consumer is demanding more and more communication speed and functionality. To meet these demands, engineers are pushing the limits of communication technology. For example, high-speed signal converters, such as analog-to-digital converters (ADCs) and digital-to-analog converters (DACs) are essential building blocks in communication technology. By sampling continuous signals, ADCs allow the signals to be processed by digital circuits. Similarly, DACs are used to generate or synthesize continuous signals from digital signals. These synthesized signals may be used as communication waveforms, such as continuous sinusoidal waves for use in conventional RF technology, or the synthesized signals may be in the form of pulses or bursts of energy for use in ultra-wideband communications.
However, many limitations must be overcome when designing very high-speed ADC's and DACs. Precise timing is crucial to these high-speed designs. One class of conventional DACs are known as “switched current source” DACs. This design uses a number of current sources that are switched when the input digital signal changes. This change in current results in a skew of the signal due to the parasitic capacitance inherent in the DAC circuit elements. At high speeds the parasitic capacitance of individual transistors (i.e., circuit blocks) can delay signals, and decrease the functionality of the DAC. Additionally, testing high-speed DACs with modern test procedures and equipment is problematic due to their complexity.
Therefore, there exists a need for apparatus and methods to construct and test converters that address the above problems and limitations.